What is Influenza (Flu) Vaccine?
There are many different kinds of influenza vaccines available in the U.S. NVIC encourages consumers to read the vaccine manufacturer's package insert information carefully before receiving influenza vaccine or any vaccine.
Standard-Dose Inactivated Flu Vaccine –
- The most common flu vaccine is the inactivated (killed) influenza vaccine, which is prepared from the fluids of chick embryos inoculated with a specific type(s) of influenza virus. 1 The strains of flu virus in the vaccine are inactivated with formaldehyde and preserved with thimerosal, which is a mercury derivative.2 (There is a limited supply of thimerosal-free or influenza vaccine with trace amounts of thimerosal and it is supplied in single dose vials, which do not require a preservative). This type of inactivated influenza vaccine is administered by injection into the muscle and contains either three (trivalent) or four (quadrivalent) influenza virus type A and type B strains.3 One trivalent flu vaccine, Afluria, is given by jet injector, a medical device which uses high pressure to administer the vaccine.4
High-Dose Trivalent Flu Vaccines -
- The high-dose trivalent influenza vaccine, Fluzone, is approved for adults age 65 and older and contains four times the amount of antigen than the standard flu vaccine.5 This vaccine is designed to hyper-stimulate the immune system to produce a stronger antibody response in the elderly.6 High-dose Fluzone is the only high-dose trivalent flu vaccine currently available in the U.S.
Recombinant Flu Vaccines -
- The recombinant flu vaccine, approved for use in 2013, is manufactured through genetic engineering.7 It is produced using insect (armyworm) cells. Flublok is the only recombinant flu vaccine currently licensed in the U.S. and one of two influenza vaccines using alternatives to chicken eggs for production.8 9
Cell-Based Flu Vaccines -
- Cell-Based flu vaccines differ from standard egg-based flu vaccines because animal cells are used to grow the influenza virus.10 Currently only one cell-based flu vaccine, Flucelvax, is available in the U.S. Licensed in 2012, it is prepared from influenza virus grown in Madin Darby canine kidney cells. This vaccine is approved for use by adults and children age 4 and older.11
Trivalent Flu Vaccine, Adjuvanted -
- In 2015, the FDA approved Fluad, the first adjuvanted trivalent flu vaccine containing a squalene oil adjuvant (MF59).12 This vaccine was approved for fast track licensure by the FDA, despite limited data on safety and immunogenicity, with approval based on a single clinical trial of about 1,000 healthy adults over the age of 65. 13 This vaccine became available for the first time to adults over the age of 65 for the 2016-2017 flu season.14
Intradermal Flu Vaccine –
- The intradermal flu vaccine was approved for use in 2012. It is an inactivated injectable influenza vaccine that is injected into the skin instead of the muscle.15 There is one quadrivalent intradermal flu vaccine available, Fluzone Intradermal, and it is licensed for use in adults aged 18 through 64. This vaccine is prepared from influenza viruses propagated in chicken embryos (unhatched baby chicks) and inactivated by formaldehyde. The intradermal flu vaccine does not contain thimerosal.16
Nasal-Spray Flu Vaccine FluMist -
- A live-virus nasal flu vaccine, FluMist, was licensed by the FDA in June 2003 and initially approved use in healthy people between the ages of 5 and 49.17 It was subsequently approved by the FDA for use in children as young as two years of age but with precautions.18 In 2014, CDC officials recommended FluMist be the influenza vaccine given to children between 2 and 8 years of age but, in 2016, the CDC recommended that FluMist not be given to children or adults of any age because the vaccine had been found to be ineffective.19 In February 2018, however, the CDC approved a new formulation of FluMist as an option for the 2018-2019 flu season despite a lack of vaccine efficacy studies.20 FluMist is prepared by introducing influenza viruses into eggs where they multiply. FluMist is a live virus vaccine and does not contain any preservatives and the vaccine will be available for the 2019/2020 flu season.21
The majority of influenza vaccines were initially designated as Category B or C pharmaceutical products. This means that adequate and well-controlled studies on pregnant women were not conducted prior to licensure of influenza vaccines and it is not known whether the vaccines can cause fetal harm when administered to a pregnant woman or can affect fertility and the reproduction capacity of a woman.
In 2015, the FDA removed pregnancy categories and replaced it with a Pregnancy and Lactation Labeling Rule.22 This rule affects all influenza vaccine products submitted after June 30, 2015. As new language is phased in, information on risks associated with vaccinating while pregnant will appear in 8.1 of each vaccine’s product insert under Risk Summary. NVIC encourages pregnant women to read this information carefully prior to receiving influenza vaccine or any other vaccine.
Below are links to the U.S. Food & Drug Administration’s (FDA) website for the most current legally-required licensing information published in manufacturer product package inserts for influenza vaccines available in the U.S. It is important to understand and read this information carefully prior to receiving a vaccine. Vaccine product package inserts contain important information about ingredients, contraindications, precautions, reported adverse reactions, safety and effectiveness data from pre-licensure clinical trials, use recommendations and more.
Quadrivalent Vaccines - Nasal
- FluMist by MedImmune, LLC
Quadrivalent Vaccines – Injected
- AFLURIA QUADRIVALENT by Seqirus Pty Ltd.
- Fluarix Quadrivalent by GlaxoSmithKline Biologicals
- Flucelvax Quadrivalent by Seqirus, Inc.
- FluLaval Quadrivalent by ID Biomedical Corporation of Quebec
- Fluzone by Sanofi Pasteur Inc.
Trivalent Vaccines - Nasal
- FluMist by MedImmune, LLC
Trivalent Vaccines - Injected
- AFLURIA by Seqirus Pty Ltd.
- FluLaval by ID Biomedical Corporation of Quebec
- Fluarixby GlaxoSmithKline Biologicals
- FLUAD by Seqirus, Inc.
- Flublokby Protein Sciences Corporation
- Flucelvaxby Seqirus, Inc.
- Fluvirin by Seqirus Vaccines Limited
- Fluzoneby Sanofi Pasteur, Inc.
IMPORTANT NOTE: NVIC encourages you to become fully informed about Influenza and the Influenza vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.
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1 CDC How Influenza (Flu) Vaccines Are Made Sept. 24, 2018
2 CDC Thimerosal in Flu Vaccine. Oct. 16, 2015
3 CDC Quadrivalent Influenza Vaccine Sept. 6, 2019
4 CDC Flu Vaccination by Jet Injector Sept. 12, 2019.
5 CDC Fluzone High-Dose Seasonal Influenza Vaccine Sept. 6, 2019
6 Simonsen L, Reichart T, Viboud C et al., Impact of Influenza Vaccination on Seasonal Mortality in the US Elderly Population Arch Intern Med 2005;165(3):265-272.
7 CDC How Influenza (Flu) Vaccines Are Made - Recombinant Flu Vaccines Sept. 24, 2018
8 CDC Recombinant Influenza (Flu) Vaccine Sept. 17, 2019
9 FDA Flublok Quadrivalent Influenza Vaccine Package Insert Jul. 2, 2019
10 CDC Cell-Based Flu Vaccines. Sept. 6, 2019
11 FDA Flucelvax Package Insert Jul. 2, 2019
12 FDA FLUAD Influenza Vaccine Package Insert Jul. 2, 2019
13NVIC Questions FDA Fast Tracking of Squalene Adjuvanted Flu Vaccine The Vaccine Reaction Sept. 16, 2016
14 CDC Flu Vaccine With Adjuvant - Flu Vaccine with Adjuvant, brand name FLUAD Sept. 4, 2019
15 CDC Intradermal Influenza (Flu) Vaccination. Oct. 31, 2018
16 FDA Fluzone Quadrivalent Intradermal Influenza Vaccine Package Insert. July 3, 2019
17 FDA June 17, 2003 Approval Letter - Influenza Virus Vaccine Live, Intranasal. June 17, 2003.
18 FDA September 19, 2007 Approval Letter - Influenza Virus Vaccine Live, Intranasal. Sept. 19, 2007.
19 CDC ACIP votes down use of LAIV for 2016-2017 flu season June 22, 2016.
20 Walker, M. ACIP Reinstates FluMist for 2018-2019 Flu Season. MEDPAGE TODAY Feb. 21, 2018
21 FDA FluMist Quadrivalent Influenza Vaccine Package Insert. July 15, 2019
22 FDA Pregnancy and Lactation Labeling (Drugs) Final Rule. Jun. 28, 2018.